the Horton-Windsor District, N. S. 169 



indigenous fauna, as red shales make up nearly one half 

 of the total mass of the sediments, and so far as known 

 are barren of fossils. In this case the extreme muddi- 

 ness of the waters, combined with probable high tempera- 

 tures (warm seas at this time are indicated by abundant 

 reef corals in western Europe), was equally deleterious 

 to animal life, 



Faiinal selection. — Unfavorable biotic conditions would 

 affect various organisms differentially. They would be 

 particularly prohibitory to the establishment of certain 

 groups of greater sensibility, such as the corals, and it is 

 not surprising that colonial corals have not been found 

 in the Windsor deposits and that cup corals are very 

 meagrely represented and gain only a temporary footing 

 in the more normal marine waters of late Windsor time. 

 .An analysis of the Windsor fauna shows that of 104 

 species belonging to 63 genera, 48 species representing 

 22 genera are brachiopods, and 36 species representing 

 25 genera are molluscs. The fauna, therefore, as deter- 

 mined by the physical environment is essentially a mollus- 

 can-brachiopod one. 



The composition of a faunal assemblage, however, is 

 dependent not only on the direct environmental factor but 

 on the available routes of migration. While the Windsor 

 faunas show very little in common with the Mississippian 

 faunas of interior America, there are clear affinities with 

 the faunas that inhabited the seas of western Europe at 

 this time. Accordingly, absentees in the Windsor faunas 

 may likewise be absent or illy represented in the Avonian 

 (Lower Carboniferous) faunas of the North Atlantic 

 province with which direct migratory relations were 

 established. This factor alone might account for the 

 meagre representation of crinoids as mere stem frag- 

 ments, for the absence of blastoids, and of such special- 

 ized bryozoans as Archimedes and Lyropora. 



Correlation with the Viseen. — In correlating the Wind- 

 sor faunas it is natural to turn in the first place to their 

 nearest allies, the Lower Carboniferous faunas of western 

 Europe. To the Belgian geologists, who were among the 

 first to illustrate these faunas, we are indebted for the 

 recognition of two major faunal divisions, the Tournai- 

 sien below and the Viseen above, corresponding approx- 

 imately to the Waverlian and Tennesseean, respectively, 

 of the American sequence. In recent years, British pal- 

 eontologists, led and inspired by the admirable studies of 



